In general, humidification of an electrolyte membrane in a fuel cell is needed to operate the fuel cell, and in this case, a humidifying apparatus is used which is operated in a manner where humid gas discharged from the fuel cell exchanges moisture with dry gas supplied from outside.
Examples of the humidifying apparatus for the fuel cell include ultrasonic humidifiers, steam humidifiers, evaporative humidifiers, and the like, and as a humidifying apparatus used for the fuel cell, a membrane humidifier, which uses a hollow fiber membrane, is generally used.
Here, a configuration and an operation of a membrane humidifier for a fuel cell in the related art will be described below.
The attached FIG. 1 illustrates an air supply system of a fuel cell system, and FIG. 2 illustrates a membrane humidifier structure included in the air supply system in the related art.
The fuel cell system includes a fuel supply system which supplies fuel (hydrogen) to a fuel cell stack, an air supply system which supplies oxygen, which is an oxidizing agent required for an electrochemical reaction and contained in air, to the fuel cell stack, a heat and water management system which controls an operating temperature of the fuel cell stack, and the fuel cell stack which substantially generates electrical energy using hydrogen and air.
Therefore, when hydrogen is supplied from the fuel supply system to a fuel electrode of the fuel cell stack, and at the same time, oxygen is supplied from the air supply system to an air electrode of the fuel cell stack, an oxidation reaction of hydrogen is carried out at the fuel electrode such that hydrogen ions (protons) and electrons are produced, and the produced hydrogen ions and electrons are moved to the air electrode through an electrolyte membrane and a separating plate, respectively. Water is produced at the air electrode caused by an electrochemical reaction among oxygen contained in air and the hydrogen ions and the electrons, which have been moved from the fuel electrode, and at the same time, electrical energy is generated from a flow of the electrons.
As illustrated in FIG. 1, the air supply system includes a membrane humidifier 100 and an air blower 202 to supply humidified air (oxygen) to a fuel cell stack 200.
Therefore, outside dry air is supplied into the hollow fiber membrane of the membrane humidifier 100 by a suction operation of the air blower 202. Simultaneously, discharge gas (humid air), which is discharged from the fuel cell stack 200 after the reaction, passes through the membrane humidifier 100, and in this case, moisture contained in the discharge gas permeates into the hollow fiber membrane such that dry air is humidified.
Referring to the attached FIG. 2, the membrane humidifier 100 in the related art includes a housing 101 which has a supply port 102 formed at one end of the housing 101 and into which dry air flows from the air blower, and a discharge port 103 formed at the other end of the housing 101 and from which humidified dry air is discharged.
In addition, a bundle of hollow fiber membranes, in which a plurality of hollow fiber membranes 106 is concentrated, are accommodated in the housing 101, and both ends of the bundle of hollow fiber membranes are accommodated by being potted by typical potting members 108.
In addition, an inlet 104 into which humid air discharged from the fuel cell stack flows is formed in one circumferential portion of the housing 101, and an outlet 105, from which humid air from which moisture has been removed is discharged, is formed in the other circumferential portion.
Therefore, when the discharge gas, which has been discharged from the fuel cell stack after the reaction is completed, that is, the humid air is supplied from the inlet 104 of the housing 101 to the hollow fiber membranes 106, moisture is separated from the humid air by a capillary action in the respective hollow fiber membranes 106. The separated moisture is condensed while passing through capillary tubes in the hollow fiber membranes 106, and then moved into the hollow fiber membranes 106.
Next, the humid air from which moisture has been separated is moved along the outside of the hollow fiber membranes 106, and then discharged through the outlet 105 of the housing 101.
At the same time, outside gas (dry air) is supplied through the supply port 102 of the housing 101 by the operation of the air blower. The dry air, which is supplied through the supply port 102, is moved through the hollow fiber membranes 106, and since the moisture separated from the humid air has been already moved into the hollow fiber membranes 106, the dry air is humidified by the moisture and the humidified dry air is supplied to the air electrode of the fuel cell stack through the discharge port 103.
Meanwhile, the fuel cell stack (hereinafter, referred to as a stack) is mounted at a position at which water (vapor condensation), which is produced at the stack during the operation of the fuel cell system or after the fuel cell system is stopped, is smoothly discharged from the stack. The reason is that in a case where condensed water flows to the stack, the condensed water blocks a part or the entirety of air flow paths (stack manifolds, cell inlet and outlet, respective channels in the cell) of the stack and hinders supply of gas (hydrogen and air) supplied at the time of starting the fuel cell or during the operation of the fuel cell, thereby causing a deterioration in performance of the stack and a potential issue with durability.
Therefore, most of the water produced at the stack inevitably flows by gravity towards a humidifier positioned at a lower end of the stack. As a result, as illustrated in the attached FIG. 3, water is collected at the bottom side in the humidifier housing 101, and the collected water is present over the inside and the outside of the potting member 108.
In addition, another reason why the condensate water is collected in the humidifier is that, as illustrated in the attached FIG. 4, dew condensation occurs due to a difference in temperature from the outside during the operation of the fuel cell at a line that connects the humidifier housing 101 and an inlet of the stack 200. The condensate water caused by the dew condensation flows downward, and then is collected in the humidifier housing.
In a case in which condensed or collected water is present in the humidifier, the water becomes frozen during the winter, and as a result, an air flow path in the humidifier becomes narrow. At the same time, pressure in the humidifier increases. For this reason, there are potential issues in that a load of the air blower for blowing air to the humidifier is increased, and power consumed by the air blower is increased.
In addition, when the water collected in the humidifier is frozen, the hollow fiber membrane, the potting member, the humidifier housing, and the like may be damaged due to volume expansion.
In addition, when output is rapidly increased (e.g., idle max. or high output), a flow velocity of air supplied to the stack may be increased such that the condensate water collected in the humidifier or attached to a surface of the humidifier also flows into the stack. As a result, there are potential issues in that flow paths in the stack are blocked, and thus cells are damaged
In consideration of the above problems, there are various related arts for discharging water collected in the humidifier housing, but as illustrated by {circle around (a)} and {circle around (b)} in FIG. 3, there is a drawback in that it may be impossible to discharge water collected in a space (a deep valley) between an outer surface of the potting member 108 and both wall surfaces of the humidifier housing 101.
The above information disclosed in this Background section is only for enhancement of understanding the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.